Conventionally, a fuel tank of an aircraft is generally formed of a metal material such as an aluminum alloy, similar to other structures constituting the aircraft. The metallic structure constituting the fuel tank in this way has a secondary function of diffusing static electricity generated due to friction with fuel to the vicinity, as well as a function of containing the fuel.
However, in recent years, a main structure of an aircraft has been made of a so-called composite material, e.g., carbon-fiber-reinforced plastic (hereinafter abbreviated as “CFRP”) from the viewpoint of weight reduction and reinforcement of the aircraft (e.g., see Patent Literature 1). This carbon-fiber-reinforced plastic structure (hereinafter abbreviated as a “CFRP structure”) is obtained by heating a carbon fiber prepreg formed by stacking a plurality of sheets each obtained by soaking a thermosetting resin into a carbon fiber to cure the thermosetting resin and unify the sheets. Further, in such a CFRP structure, a so-called resin layer is formed on a surface of the structure by a thermosetting resin exuded from a carbon fiber when the carbon prepreg is heated.